There are over 30 elements you can use to build your circuits. The app has everything from simple resistors, to switches, to MOSFETS, to digital gates.

The app features a multimeter that you use to probe around the circuit to instantly read voltages and currents. If you want to see how a value changes over time, then you can add values to the built-in oscilloscope. The scope can simultaneously track many signals over time and features a touch interface to control the total time displayed and stacked and unstacked modes to easily compare signals.

Supported elements include:

Signal generators, Voltage sources, and Current sources

Resistors, Capacitors, and inductors

Manual SPST/SPDT Switches, and SPST/SPDT relays

Diodes, BJ Transistors, and MOSFETs

Speakers, Buzzers, and LEDs

ADCs, and DACs

Logic gates: AND, OR, NAND, NOR, XOR

JK and D Flip-flops

I gave the app a quick spin on the iPad, and it definitely shows a lot of potential. The simulator had a tendency to lag a bit behind my realtime changes to the schematic, and the UI took some getting used to, but for $10 it sure beats the mobile simulator competition (which is pretty much nonexistent, to my knowledge).

In any case – a handy tool to have around when away from the lab. As the developer notes, the software is rather CPU-intensive so newer devices are recommended (iPhone 3GS or later). iCircuit on iTunes